It is known at internal combustion engines used within a relatively broad range of revolutions, that the gas volume sucked in at a certain number of revolutions can be increased by tuning the length and diameter of the inlet pipes, thereby also increasing the so-called volumetric efficiency of the engine. This depends on, that the gas quantity present in the intake system is influenced by the operating frequency of the inlet valves, so that the gas comes in resonance oscillation. When the oscillation period corresponds to the operating frequency of the valves, the abovementioned increase of the volumetric efficiency is obtained. Consequently, at certain numbers of revolution a higher volumetric efficiency is achieved with a long inlet pipe, whereas at other numbers of revolution a short inlet pipe gives a higher volumetric efficiency.
It is also earlier known, for example from EP 0182223, to provide an extra air distribution chamber, which is placed between the first distribution chamber and the inlet valves and which is connected to each inlet pipe via an openable throttle. By means of this arrangement the efficient length on the inlet pipes can be varied, whereby opening of the throttles gives an increase of the volumetric efficiency within a higher range of revolutions.
It is desirable to place the point for transition from the first adjustment stage to the second adjustment stage at such a point and with such overlapping of the two curves, that no marked drop in torque is experienced, in said transition area. Hereby the positive effect of these known arrangements in reality becomes rather limited.